1. Field of the Invention
The present invention relates to a method for compensating scattered signal output characteristics of a multiple-element type infrared detector employed in a thermal imaging system.
2. Description of the Related Art
InSb (indium-antimony), HG.sub.1-x Cd.sub.x Te (mercury-cadmium-tellurium), etc. have been employed as infrared detector elements inafrared detector apparatus. The scattered characteristics of the elements are individually adjusted with an electric circuit connected to each element or numerically adjusted with a program installed in the apparatus.
In the above-described prior art thermal imaging system, a reference plate having a temperature almost equal to the temperature of the temperature image detecting apparatus is temporarily placed so as to obstruct the light path to the the reference plate is typically placed in front of the infrared camera, in order to input an equal light to all of the detector elements. Then, amounts of compensating of DC (direct current) offsets of the individual detector elements are determined from output signal levels of the respective detector elements while the equal light is thus input thereto. The amounts of compensation of DC offsets are then stored in a memory device. Next, in the practical operation of the apparatus, the reference plate is removed so that a scene to be monitored is input to the camera. Then, the thermal image is constituted or constructed with the detector output signals whose DC offsets are compensated by being added with the thus determined amounts of compensation read out of the memory.
The prior art thermal imaging system however, has the following problems. First, temperature of the reference plate is not always equal or close to the thermal range of the practical scene to be monitored. Therefore, the compensation for the scene, which generally was a thermal range different from the reference plate temperature, cannot always be accurately achieved by the DC offset compensation using the reference plate having the certain fixed temperature. Moreover, a mechanism required to place/remove the reference plate into or out of the light path becomes large as well as requires troublesome and time-consuming work.